Electric motor for a power tool

ABSTRACT

An electric motor includes first and second balancing members coupled to an output shaft for rotation with a rotor. The first and second balancing members substantially balance a mass of the rotor about a longitudinal axis of the output shaft to reduce vibrations of the electric motor during use. The first balancing member includes a brass bushing supported on the output shaft adjacent a first face of the body of the rotor. The brass bushing includes a hole drilled into an outer circumference of the brass bushing providing a first balancing feature of the electric motor. The second balancing member includes a fan supported on the output shaft adjacent a second face of the body of the rotor. The fan includes a plurality of fins extending from a first face of the fan and a second balancing feature of material removed from a second face of the fan.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation patent application to U.S.application Ser. No. 14/072,023, filed Nov. 5, 2013, and claims priorityto U.S. Provisional Patent Application No. 61/723,166, filed Nov. 6,2012, the entire contents of which are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to power tools and, more particularly, toelectric motors for use with power tools.

BACKGROUND OF THE INVENTION

Many power tools use electric motors, such as brushless DC motors, todrive the tools. A brushless DC motor typically includes a rotor and astator. During operation, the rotor rotates at a relatively high speedrelative to the stator. If the motor is unbalanced, the power tool mayvibrate or shake during use.

SUMMARY OF THE INVENTION

In one embodiment, the invention provides an electric motor for use witha power tool. The motor includes a rotor having a body and a pluralityof magnets coupled to the body, a stator having a plurality ofelectromagnetic coils surrounding the rotor, and an output shaft coupledto the rotor for rotation with the rotor. The output shaft defines alongitudinal axis about which the rotor rotates. The motor also includesa balancing member coupled to the output shaft for rotation with therotor. The balancing member substantially balances a mass of the rotorabout the longitudinal axis to reduce vibrations of the electric motorduring use.

In another embodiment, the invention provides a power tool including ahousing, a drive mechanism positioned within the housing, and anelectric motor positioned within the housing and operable to drive thedrive mechanism. The motor includes a rotor having a body and aplurality of magnets coupled to the body, a stator having a plurality ofelectromagnetic coils surrounding the rotor, and an output shaft coupledto the rotor for rotation with the rotor and coupled to the drivemechanism to drive the drive mechanism. The output shaft defines alongitudinal axis about which the rotor rotates. The motor also includesa balancing member coupled to the output shaft for rotation with therotor. The balancing member substantially balances a mass of the rotorabout the longitudinal axis to reduce vibrations of the electric motorduring use.

In some embodiments, the balancing member includes at least one of abushing having a balancing feature formed on the bushing, an overmold onthe shaft having a balancing feature formed on the overmold, a bushinghaving a slot that receives an insert of balancing material, a fanhaving a balancing feature formed on the fan, and a fan having a slotthat receives an insert of balancing material.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a power tool with a portion of a housingremoved to show a motor.

FIG. 2 is a perspective view of the motor shown in FIG. 1.

FIG. 3 is a perspective view of a motor including a bushing.

FIG. 4 is a perspective view of the motor and the bushing of FIG. 3 witha balancing feature formed on the bushing.

FIG. 5 is a side view of the motor and the bushing of FIG. 3.

FIG. 6 is a perspective view of a motor shaft before and after the shaftis overmolded.

FIG. 7 is a perspective view of a motor including the overmolded shaftof FIG. 6.

FIG. 8 is a perspective view of a motor including a bushing with slots.

FIG. 9 is an end view of the motor and the bushing of FIG. 8.

FIG. 10 is a perspective view of a motor including a fan.

FIG. 11 is a perspective view of the motor and the fan of FIG. 10 with abalancing feature formed on the fan.

FIG. 12 is a perspective view of the motor and the fan of FIG. 10 with abalancing feature formed on a bushing that supports the fan.

FIG. 13 is a perspective view of a motor including a fan with slots.

FIG. 14 is an end view of the motor and the fan of FIG. 13.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways.

DETAILED DESCRIPTION

FIG. 1 illustrates a power tool 10 including an electric motor 14, suchas a brushless DC motor. In the illustrated embodiment, the power tool10 is a hammer drill. In other embodiments, the power tool 10 may be,for example, a reciprocating saw, a circular saw, a jigsaw, a drill, animpact driver, a screwdriver, a pipe cutter, a grinder, a sander, acaulk gun, a grease gun, or the like. In further embodiments, the powertool 10 may be another type of device that uses an electric motor, suchas a vacuum, a paint sprayer, lawn and garden equipment, or the like.

The motor 14 is positioned in a housing 18 of the power tool 10 andconnected to a drive mechanism 22. The illustrated power tool 10 alsoincludes a battery connection portion 26 formed on the housing 18. Thebattery connection portion 26 receives a battery pack to electricallycouple the battery pack to the motor 14 through a switch and otherelectronics. The battery pack may be, for example, a 9V, 12V, 18V, 28V,or 36V Li-ion or NIMH battery pack. When powered, the electric motor 14drives the drive mechanism 22 to operate a working element (e.g., adrill bit) connected to a chuck 30 of the power tool 10.

FIG. 2 illustrates the electric motor 14 in more detail. The motor 14includes a rotor 34, a stator 38, and a motor shaft 42. The rotor 34includes four permanent magnets 46 positioned in a body 50, or stack, ofthe rotor 34. The body 50 may be a laminated steel structure or powderedsteel. The illustrated magnets 46 are received in corresponding slots 54formed in the body 50 and extend between a first face 50A and a secondface 50B (FIG. 5) of the body 50. The slots 54 are arranged generallyperpendicular to one another in a square pattern in the body 50. Theillustrated stator 38 includes six electromagnetic coils 58 surroundingthe rotor 34. The coils 58 are surrounded by laminations 60 of thestator 38. When powered, the electromagnetic coils 58 create magneticfields that interact with the permanent magnets 46 in the rotor 34 torotate the rotor 34 relative to the stator 38. In other embodiments, themotor 14 may include fewer or more permanent magnets 46 in the rotor 34and/or electromagnetic coils 58 in the stator 38. Although theillustrated magnets 46 are positioned within the rotor body 50 such thatthe magnets 46 are interior permanent magnets (IPM), in otherembodiments the magnets 46 may be glued or otherwise affixed onto anouter surface of the rotor body 50 such that the magnets 46 are surfacepermanent magnets (SPM).

The motor shaft 42, or output shaft, extends out of the rotor 34 torotate with the rotor 34. The shaft 42 defines a longitudinal axis 68about which the rotor 34 rotates. The shaft 42 is fixed to the rotor 34such that movement of the rotor 34 is transmitted to the shaft 42. Insome embodiments, the shaft 42 may be fixed to the rotor 34 usingsuitable securing means, such as splines, knurls, press-fitting,adhesives, or the like. In other embodiments, a portion of the shaft 42may be non-cylindrical to rotationally fix the shaft 42 to the rotor 34.

A first bearing 70 is positioned on a first end of the shaft 42 tosupport the shaft 42, and thereby the motor 14, within the housing 18 ofthe power tool 10. A fan or impeller 74 is coupled to a second end ofthe shaft 42 to rotate with the shaft 42 and the rotor 34. The fan 74creates an airflow around the motor 14 to cool the motor 14 duringoperation of the power tool 10. A second bearing 78 (FIG. 5) is coupledto the second end of the shaft 42 adjacent the fan 74 to help supportthe motor 14 in the housing 18 of the power tool 10.

FIG. 3 illustrates a similar motor 114 including the rotor 34, thestator (not shown), the motor shaft 42, and the fan 74. In thisembodiment, the motor 114 includes a balancing member 118 comprising abushing 122. The illustrated bushing 122 is generally cylindrical andcomposed of a non-magnetic, high density material such as brass. Thebushing 122 is coupled to the shaft 42 between the first face 50A of therotor body 50 and the bearing 70 (FIG. 5). The bushing 122 is fixed tothe shaft 42 to rotate with the rotor 34 and the shaft 42 relative tothe stator. In some embodiments, the bushing 122 may be secured to theshaft 42 by splines, knurls, press-fitting, or the like.

When the bushing 122 is assembled on the shaft 42, the bushing 122rotates with the rotor 34 to help balance the motor 114. If the motor114 is still imbalanced, a balancing feature 126 (FIG. 4) is formed onthe bushing 122 to correct the imbalance within a predeterminedspecification. As shown in FIG. 4, the illustrated balancing feature 126is machined in the bushing 122 by drilling a hole into an outercircumferential surface 130 of the bushing 122. In other embodiments,other balancing features may be formed on the bushing 122 by cutting,shaving, or otherwise removing material from the bushing 122.Additionally or alternatively, multiple balancing features may be formedon the bushing 122 to balance the motor 114 within the predeterminedspecification.

As shown in FIG. 5, the bushing 122 also includes a flange or step 134.The step 134 has a smaller diameter than the remainder of the bushing122 and extends axially from the bushing 122. The step 134 engages thebearing 70 to help support the bearing 70 on the shaft 42. Inparticular, the step 134 supports an inner face of the bearing 70 toprevent the bearing 70 from moving along the shaft 42 toward the rotorbody 50 if the power tool is dropped or during high vibration tool use.In some embodiments, the step 134 may be omitted.

FIGS. 6 and 7 illustrate another motor 214 including the rotor 34, thestator (not shown), the motor shaft 42, and the fan 74. In thisembodiment, the motor 214 includes a balancing member 218 comprising anovermold 222 on the shaft 42. FIG. 6 illustrates the shaft 42 before andafter the overmold 222 is applied to the shaft 42. In the illustratedembodiment, the overmold 222 is a thermoset plastic or thermoplasticmaterial molded over a knurled surface 226 of the shaft 42. In otherembodiments, other suitable materials may also or alternatively bemolded over the shaft 42. In still other embodiments, the overmold 222could be molded over the shaft 42, the magnets 46, and the rotor body 50or over the shaft 42 and the rotor body 50.

The illustrated overmold 222 includes a radially-extending flange 230having a larger diameter than the remainder of the overmold 222. Theflange 230 is formed near, but spaced from an end of the overmold 222adjacent a first end of the shaft 42. The flange 230 provides a hardstop for the rotor body 50. In some embodiments, the flange 230 may alsoprovide a hard stop for the bearing (not shown) positioned on the firstend of the shaft 42. In such embodiments, the bearing may be positionedon a smaller diameter section 234 of the overmold 222. In otherembodiments, the smaller diameter section 234 of the overmold 222 mayabut the bearing to provide the hard stop.

Referring to FIG. 7, the rotor body 50 is pressed onto the overmold 222to fix the body 50 and the shaft 42 together. The first face 50A of thebody engages an inner face 238 (FIG. 6) of the flange 230 to inhibitaxial movement of the body 50 along the overmold 222. In addition, theremainder of the overmold 222 provides a press surface for laminationsof the rotor body 50.

When the overmold 222 is formed on the shaft 42, the overmold 222 helpsbalance the motor 214. In some embodiments, one or more balancingfeatures may be formed on the overmold 222 (particularly in theradially-extending flange 230 of the overmold 222) to help correct anyimbalances of the motor 214. For example, material may be cut, drilled,shaved or otherwise removed from the overmold 222 to balance the motor214 within the predetermined specification.

In some embodiments, the balancing member 218 may also include a balancewasher or bushing coupled to the overmold 222. The balance washer may beinsert molded into the overmold 222 or may be assembled onto theovermold 222 (e.g., over the smaller diameter section 234 of theovermold 222 adjacent the first end of the shaft 42). In furtherembodiments, one or more balancing features may also or alternatively beformed in the washer to help balance the motor 214.

FIG. 8 illustrates another motor 314 including the rotor 34, the stator(not shown), the motor shaft 42, and the fan 74. In this embodiment, themotor 314 includes a balancing member 318 comprising a slotted bushing322. The illustrated bushing 322 is generally cylindrical and composedof a non-magnetic material such as brass or plastic. The bushing 322 iscoupled to the shaft 42 between the first face 50A of the rotor body 50and the bearing (not shown). The bushing 322 is fixed to the shaft 42 torotate with the rotor 34 and the shaft 42 relative to the stator. Insome embodiments, the bushing 322 may be secured to the shaft 42 bysplines, knurls, press-fitting, or the like.

In the illustrated embodiment, the bushing 322 includes wedge-shapedopenings or slots 326 extending through the bushing 322. The illustratedbushing 322 includes fourteen slots 326 formed in a face of the bushing322 and arranged circumferentially about the longitudinal axis 68. Inother embodiments, the bushing 322 may include fewer or more slots 326.The slots 326 are separated by radially-extending sidewalls 330 suchthat each slot 326 is discrete from adjacent slots 326.

As shown in FIG. 9, a wedge-shaped insert 334 of balancing material ispositioned within one of the slots 326 of the bushing 322. In someembodiments, the balancing material is a putty or soft epoxy thathardens and sets in the slot 326. In other embodiments, the insert 334may be a separate piece that is shaped to generally match the shape ofthe slots 326 and is held in the corresponding slot 326 by press-fittingand/or adhesives. When positioned in the slot 326, the insert 334 iscaptured between the first face 50A of the rotor 34 and the bearing toinhibit the insert 334 from sliding out of the bushing 322. The bushing322 and the insert 334 help correct imbalances in the motor 314 when therotor 34 rotates relative to the stator. Although only one insert 334 isshown in one slot 326 of the bushing 322, it should be readily apparentthat multiple inserts 334 may be positioned in multiple slots 326 tohelp balance the motor 314 within the predetermined specification.

In other embodiments, the slots 326 may be formed in an overmoldcovering the motor shaft 42, such as the overmold 222 shown in FIGS. 6and 7. In such embodiments, the inserts 334 of balancing material may bepositioned directly in the overmold, rather than in the bushing 322. Thebushing 322 may therefore be omitted or may be used in combination withthe overmold.

FIG. 10 illustrates another motor 414 including the rotor 34, the stator(not shown), the motor shaft 42, and the fan 74. In this embodiment, themotor 414 includes a balancing member 418 comprising the fan 74. Asdiscussed above, the fan 74 rotates with the rotor 34 and the shaft 42to create an airflow for cooling the motor 414 during operation. Bladesor fins 422 extend from a first face 426 of the fan 74 to generate theairflow. In the illustrated embodiment, the fan 74 is seated on abushing 430 that surrounds a portion of the shaft 42 adjacent the secondface 50B of the rotor body 50. In some embodiments, the bushing 430 maybe part of an overmold formed on the shaft 42, such as the overmold 222shown in FIGS. 6 and 7.

As shown in FIG. 11, a balancing feature 434 is formed on a second face438 of the fan 74 opposite the fins 422. The balancing feature 434 helpsbalance the motor 414 within the predetermined specification. In theillustrated embodiment, the balancing feature 434 is machined in the fan74 by cutting material off of the second face 438 of the fan 74. Inother embodiments, other balancing features may be formed on the fan 74by drilling, shaving, or otherwise removing material from the fan 74.Additionally or alternatively, multiple balancing features 434 may beformed on the fan 74 to balance the motor 414 within the predeterminedspecification.

As shown in FIG. 12, a balancing feature 442 is formed on an outer face446 of the bushing 430. The balancing feature 442 helps balance themotor 414 within the predetermined specification. In the illustratedembodiment, the balancing feature 442 is machined in the bushing 430 bydrilling a hole into the outer face 446 of the bushing 430. In otherembodiments, other balancing features may be formed on the bushing 430by cutting, shaving, or otherwise removing material from the bushing430. Additionally or alternatively, multiple balancing features 442 maybe formed on the bushing 430 to balance the motor 414 within thepredetermined specification. In further embodiments, balancing featuresmay be formed on both the fan 74 and the bushing 430 to help balance themotor 414.

FIG. 13 illustrates another motor 514 including the rotor 34, the stator(not shown), and the motor shaft 42. In this embodiment, the motor 514includes a balancing member 518 comprising a slotted fan 522. Theillustrated fan 522 is similar to the fan 74 discussed above, but alsoincludes wedge-shaped openings or slots 526. The slots 526 are formed ina face 530 of the fan 522 opposite from fins 534 of the fan 522. In theillustrated embodiment, the slots 526 are formed in an inner radialportion of the face 530. In other embodiments, the slots 526 may beformed in an outer radial portion of the face 530. The illustrated fan522 includes fourteen slots formed in the face 530 of the fan 522 andarranged circumferentially about the longitudinal axis 68. In otherembodiments, the fan 522 may include fewer or more slots 526. The slots526 are separated by radially-extending sidewalls 538 such that eachslot 526 is discrete from adjacent slots 526.

As shown in FIG. 14, a wedge-shaped insert 542 of balancing material ispositioned within one of the slots 526 of the fan 522. In someembodiments, the balancing material is a putty or soft epoxy thathardens and sets in the slot 526. In other embodiments, the insert 542may be a separate piece that is shaped to generally match the shape ofthe slots 526 and is held in the corresponding slot 526 by press-fittingand/or adhesives. The insert 542 helps correct imbalances in the motor514 when the rotor 34 rotates relative to the stator. Although only oneinsert 542 is shown in one slot 526 of the fan 522, it should be readilyapparent that multiple inserts 542 may be positioned in multiple slots526 to help balance the motor 514 within the predeterminedspecification.

The balancing members 118, 218, 318, 418, 518 discussed above helpbalance an electric motor in a power tool, or other device, within apredetermined specification to reduce vibration of the motor during use.In particular, the balancing members 118, 218, 318, 418, 518 balancemasses of the corresponding rotors about the longitudinal axis of themotors (e.g., about the longitudinal axis 68) to reduce vibrations ofthe motors compared to motors without balancing members. Although eachof the balancing members 118, 218, 318, 418, 518 has been describedseparately, a single motor may include a combination of two or more ofthe balancing members 118, 218, 318, 418, 518 to achieve the desiredbalance.

Although the invention has been described with reference to certainpreferred embodiments, variations and modifications exist within thescope and spirit of one or more independent aspects of the invention asdescribed.

What is claimed is:
 1. An electric motor for the use with a power tool,the electric motor comprising: a rotor including a body and a pluralityof magnets coupled to the body; a stator including a plurality ofelectromagnetic coils surrounding the rotor; an output shaft coupled tothe rotor for rotation with the rotor, the output shaft defining alongitudinal axis about which the rotor rotates; and first and secondbalancing members coupled to the output shaft for rotation with therotor, the first and second balancing members substantially balancing amass of the rotor about the longitudinal axis to reduce vibrations ofthe electric motor during use; wherein the first balancing memberincludes a brass bushing supported on the output shaft adjacent a firstface of the body of the rotor, the brass bushing including a holedrilled into an outer circumference of the brass bushing providing afirst balancing feature of the electric motor; and wherein the secondbalancing member includes a fan supported on the output shaft adjacent asecond face of the body of the rotor, the fan including a plurality offins extending from a first face of the fan and a second balancingfeature of material removed from a second face of the fan.
 2. Theelectric motor of claim 1, further comprising a bearing supported on theoutput shaft, wherein the first balancing member is located between thefirst face of the body of the rotor and the bearing.
 3. The electricmotor of claim 1, wherein the first balancing feature is formed on thebrass bushing after the brass bushing is assembled on the output shaft.4. The electric motor of claim 1, wherein the fan is supported on asecond bushing that surrounds a portion of the output shaft adjacent thesecond face of the body of the rotor.
 5. A power tool comprising: ahousing; a drive mechanism positioned within the housing; and anelectric motor positioned within the housing and operable to drive thedrive mechanism, the motor including a rotor including a body and aplurality of magnets coupled to the body, a stator including a pluralityof electromagnetic coils surrounding the rotor, an output shaft coupledto the rotor for rotation with the rotor and coupled to the drivemechanism to drive the drive mechanism, the output shaft defining alongitudinal axis about which the rotor rotates, and first and secondbalancing members coupled to the output shaft for rotation with therotor, the first and second balancing members substantially balancing amass of the rotor about the longitudinal axis to reduce vibrations ofthe electric motor during use; wherein the first balancing memberincludes a brass bushing supported on the output shaft adjacent a firstface of the body of the rotor, the brass bushing including a holedrilled into an outer circumference of the brass bushing providing afirst balancing feature of the electric motor; and wherein the secondbalancing member includes a fan supported on the output shaft adjacent asecond face of the body of the rotor, the fan including a plurality offins extending from a first face of the fan and a second balancingfeature of material removed from a second face of the fan.
 6. The powertool of claim 5, wherein the motor further includes a bearing supportedon the output shaft, and wherein the first balancing member is locatedbetween the first face of the body of the rotor and the bearing.
 7. Thepower tool of claim 5, wherein the first balancing feature is formed onthe brass bushing after the brass bushing is assembled on the outputshaft.
 8. The power tool of claim 5, wherein the fan is supported on asecond bushing that surrounds a portion of the output shaft adjacent thesecond face of the body of the rotor.